Abstract
BackgroundDuring the bread wheat speciation by polyploidization, a series of genome rearrangement and sequence recombination occurred. Simple sequence repeat (SSR) sequences, predominately located in heterochromatic regions of chromosomes, are the effective marker for tracing the genomic DNA sequence variations. However, to date the distribution dynamics of SSRs on chromosomes of bread wheat and its donors, including diploid and tetraploid Triticum urartu, Aegilops speltoides, Aegilops tauschii, Triticum turgidum ssp. dicocoides, reflecting the genome evolution events during bread wheat formation had not been comprehensively investigated.ResultsThe genome evolution was studied by comprehensively comparing the distribution patterns of (AAC)n, (AAG)n, (AGC)n and (AG)n in bread wheat Triticum aestivum var. Chinese Spring and its progenitors T. urartu, A. speltoides, Ae. tauschii, wild tetroploid emmer wheat T. dicocoides, and cultivated emmer wheat T. dicoccum. Results indicated that there are specific distribution patterns in different chromosomes from different species for each SSRs. They provided efficient visible markers for identification of some individual chromosomes and SSR sequence evolution tracing from the diploid progenitors to hexaploid wheat. During wheat speciation, the SSR sequence expansion occurred predominately in the centromeric and pericentromeric regions of B genome chromosomes accompanied by little expansion and elimination on other chromosomes. This result indicated that the B genome might be more sensitive to the “genome shock” and more changeable during wheat polyplodization.ConclusionsDuring the bread wheat evolution, SSRs including (AAC)n, (AAG)n, (AGC)n and (AG)n in B genome displayed the greatest changes (sequence expansion) especially in centromeric and pericentromeric regions during the polyploidization from Ae. speltoides S genome, the most likely donor of B genome. This work would enable a better understanding of the wheat genome formation and evolution and reinforce the viewpoint that B genome was originated from S genome.
Highlights
During the bread wheat speciation by polyploidization, a series of genome rearrangement and sequence recombination occurred
The epigenetic changes are mainly associated with methylation changes, while the genetic changes mainly involve a large number of sequence removal, genome rearrangements, rewiring of gene expression, and chromosome instability [4, 7,8,9]
No obvious signals were observed on D genome chromosomes (Fig. 4f)
Summary
During the bread wheat speciation by polyploidization, a series of genome rearrangement and sequence recombination occurred. Upon merging two or more different genomes into one nucleus, the nascent polyploid faces several challenges such as rescheduling chromosome pairing, gene expression and DNA replication, and reducing the cost of large genomes To meet these challenges, the polyploid genome must undergo a series of genetic and epigenetic changes [2,3,4,5,6,7]. The epigenetic changes are mainly associated with methylation changes, while the genetic changes mainly involve a large number of sequence removal, genome rearrangements, rewiring of gene expression, and chromosome instability [4, 7,8,9] All these events occurred immediately after polyploid formation, or on an evolutionary scale [7, 8, 10]. Polyploidization is an important source of stress that facilitates rapid genome evolution
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